It is well known that the components of most pneumatic tire constructions must be assembled in a way, which promotes tire uniformity in order to provide optimum tire performance. Tire uniformity is generally considered to mean tire dimensions and mass distributions which are uniform and symmetric in all directions, so that there is static and dynamic balance of forces.
Although certain degrees of tire nonuniformity can be corrected in post assembly manufacturing, it is more preferable and more efficient to build a more uniform tire. Typically, tires are constructed on a tire building drum, around which the tire components are wrapped in successive layers such as an innerliner, one or more reinforced carcass plies, optional sidewalls, bead area inserts or apexes, sidewalls and bead wires. Typically, the innerliner and the ply layer are each wrapped around the drum and then the ends are cut and spliced together. Tire manufacturers typically strive to balance the splices around the tire to minimize tire nonuniformity.
Tire manufacturers typically make their own ply, wherein the ply is made from reinforcement filaments or cords, which are woven into a fabric wherein the cords run longitudinally along the length of the fabric. A pic cord runs across the width of the ply to maintain the spacing or epi (ends per inch) of the cords. This ply fabric is then coated with a rubber adhesive and calendered. The coated fabric is then sheared into discrete segments having a length matching the desired width needed to make a tire. The lateral edges of these segments are then spliced together, wherein the cords are transverse to the length of the spliced together segments. A plurality of segments is spliced together in order to achieve the necessary circumferential length needed for a specified tire. These preparatory splices typically overlap several cords, because the edges of the segments are not perfectly straight. Generally, there are two to three preparatory splices in a ply tire component, in addition to the final splice used to mount the ply on the tire manufacturing drum.
One disadvantage to the prior art process is that multiple splices are needed, which can contribute to tire nonuniformity, especially where the splices overlap cord, creating a very small increase in mass as well as more strength, less flexibility at a discrete location. Another disadvantage is that the exact spacing of the cord at the ends of the ply tire component can vary slightly, typically “bunching up” or increasing in epi resulting in more strength, less flexibility which could create an undulation in the tire sidewall. Further, the pic cord can also contribute to tire nonuniformity. A further disadvantage to the prior art process is that if the tire manufacturer needs to change the type or size of tire in production on a given drum, the spools of tire ply component will also need to be changed. Still further yet, there has been an increasing trend in high performance tires to use a tire ply component wherein the cords have a slight angle variation (generally ply runs radially from bead to bead at 90 degrees) to 88 degrees or some other desired angular variation. It is much more difficult to manufacture ply with an angular variation using the prior art processes.
Thus an improved method and apparatus of making a more uniform ply component for a tire having a uniform number of cords and uniform spacing of cords wherein there are no detectable splices. It is further desired to have a method and apparatus to manufacture ply wherein the gauge, width, cord angle and cord spacing may be easily changed without downtime of the machine. It is further desired to make the ply at the tire building drum, as there has been an increasing trend among tire manufacturers to be able to manufacture a variety of tires on a tire building machine without undue delay in switchovers.